Transverse electric-field type liquid crystal display device, process of manufacturing the same, and scan-exposing device

ABSTRACT

A process of manufacturing a liquid crystal display device of transverse electric-field type, wherein a halftone photomask which is used to form a photoresist pattern has a fully light-shielding area preventing UV irradiation of a portion of an active matrix substrate in which a thin-film transistor element is to be formed, so that the photoresist pattern includes a positive resist portion which has a first thickness and which is formed on the above-indicated portion of the substrate. The halftone mask further has a fully light-transmitting area which permits fully UV transmission therethrough to provide the photoresist pattern with a resist-free area which corresponds to a portion of the substrate in which a contact hole serving as a third connection portion connecting an external scanning-line driver circuit and a scanning-line terminal portion through a junction electrode is to be formed. The photoresist pattern also has a positive resist portion which is formed in the other portion of the substrate and which has a second thickness smaller than the first thickness. Also disclosed in a scan-exposing device used in the process is also disclosed.

This is a continuation of U.S. patent application Ser. No. 12/220,781,filed Jul. 28, 2008 which is a continuation of U.S. patent applicationSer. No. 11/249,596, filed Oct. 13, 2005 which is a continuation ofprior U.S. patent application Ser. No. 10/606,175 filed Jun. 25, 2003now U.S. Pat. No. 7,125,654 claiming the benefit of Japanese ApplicationNo. 2002-237219 filed Jul. 1, 2002, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display device oftransverse electric-field type which is available at a relatively lowcost and which permits high-quality displaying of images on a widescreen with a wide field of view or a large angle of visibility. Thepresent invention is further concerned with a process of manufacturingsuch a liquid crystal display device, and a scan-exposing device used inthe process of manufacture.

BACKGROUND OF THE INVENTION

JP-A-2000-066240 (Laid-open Publication of Japanese Patent Application)discloses a halftone exposure technique effective to reduce the requirednumber of steps in a photomasking process in the manufacture of a liquidcrystal display device of active matrix type. The halftone exposuretechnique disclosed in this publication uses a slit-type photomask 70which has slits 73 formed in its local portions, as shown in FIG. 1. Thelocally formed slots 73 serve to adjust an average amount of exposure ofan active matrix substrate 9 to a light generated by an exposing device,for forming a first pattern of a resist on a portion of the substrate 9which corresponds to a channel portion of a thin-film transistor. Thefirst pattern of resist has a positive resist portion 6 having arelatively large thickness and a positive resist portion 7 having asmaller thickness than that of the positive resist portion 6. Then, anetching operation is performed on the substrate 9 so that only thoseportions of semiconductor layers 10, 11, a barrier metal layer 12 and alow-resistance metal layer 13 which underlie the positive resistportions 6, 7 of the first resist pattern are left, whereby thesemiconductor layers 10, 11 are formed into semiconductor elements. Thethickness of the positive resist portions 6, 7 are then reduced by anashing operation, so that the positive resist portion 7 in the areacorresponding to the channel portion of the thin-film transistor elementis removed, with a result of formation of a second resist pattern whichconsists of only the positive resist portions 6. The channel portion ofthe thin-film transistor element is formed by etching using the secondresist pattern. According to the halftone exposure technique disclosedin JP-A-2000-066240 described above, a single photomasking step permitsformation of the semiconductor layers into the semiconductor elements,and formation of the channel portion of the thin-film transistorelement. Accordingly, the halftone exposure technique makes it possibleto reduce the required number of the photomasks, and considerably lowerthe cost of manufacture of the active matrix substrate, as compared withthe conventional photomasking technique. The halftone exposure techniqueof JP-A-200-066240 is shown in FIG. 22.

Where the halftone exposure technique as disclosed in JP-A-2000-066240is used to form the channel portion of the thin-film transistor element,however, the formed channel portion of the thin-film transistor elementtends to have a relatively large amount of variation in its dimensionalaccuracy, leading to instability factors in mass production of a productincluding the thin-film transistor elements. Further, a variation in theamount of overlapping between a gate electrode and source and drainelectrodes causes a display variation in the halftone area, giving riseto a problem of reduction in the yield ratio of the active matrixsubstrate.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide aprocess which permits economical high-yield manufacture of a liquidcrystal display device of transverse electric-field type which has aconsiderably large size and a considerably wide field of view. A secondobject of the invention is to provide such a liquid crystal displaydevice. A third object of the invention is to provide a scan-exposingdevice used in the process of manufacture according to the presentinvention.

The first object may be achieved according to a first aspect of thisinvention, which provides a process of manufacturing a liquid crystaldisplay device of transverse electric-field type including (a) a pair ofsubstrates at least one of which is transparent, (b) a layer of a liquidcrystal composition interposed between the pair of substrates, (c) aplurality of scanning lines driven by an external scanning-line drivercircuit through scanning-line terminal portions and extending in a linedirection, (d) a plurality of image-signal wires extending in a columndirection, (e) picture-element electrodes corresponding to respectivepicture elements, (f) common electrodes cooperating with thepicture-element electrodes, and (g) thin-film transistor elementsconnected to the scanning lines and the image-signal wires, and whereinscanning lines, the image-signal wires, the picture-element electrodes,the common electrodes and the thin-film transistor elements are providedon a surface of one of the pair of substrates which faces the layer ofthe liquid crystal composition, the process being characterized bycomprising:

a halftone exposing step of exposing a photoresist on theabove-indicated one of the pair of substrates to a radiation, andthereby forming (i) first positive resist portions that cover portionsof a semiconductor layer formed on the above-indicated one substrate,which portions correspond to the thin-film transistor elements, each ofthe first positive resist portions having a predetermined firstthickness, (ii) resist-free portions that cover portions of thesemiconductor layer which correspond to a first connecting portion, asecond connecting portion and a third connecting portion, the firstconnecting portion being provided to form first static-electricityprotective transistor elements connecting the common electrodes and thescanning lines, the second connecting portion being provided to formsecond static-electricity protective transistor elements connecting thecommon electrodes and the image-signal wires, and the third connectingportion connecting the external scanning-line driver circuit and thescanning-line terminal portions, and (iii) second positive resistportions having a second thickness smaller than the first thickness andcovering the other portions of the semiconductor layer.

In the process of manufacturing a liquid crystal display device oftransverse electric-field type according to the first aspect of theinvention, the halftone exposing step is implemented to form (i) thefirst positive resist portions which have the first thickness and whichcover the portions of the semiconductor layer which correspond to thethin-film transistor elements, (ii) the resist-free areas covering theportions of the semiconductor layer which correspond to the firstconnecting portion provided to form the first static-electricityprotective transistor elements connecting the common electrodes and thescanning lines, the second connecting portion provided to form thesecond static-electricity protective transistor elements connecting thecommon electrodes and the image-signal wires, and the third connectingportion connecting the external scanning-line driver circuit and thescanning-line terminal portions, and (iii) the second positive resistportions which have a second thickness smaller than the first thicknessand which cover the other portions of the semiconductor layer.Accordingly, the portions of the semiconductor layer corresponding tothe first, second and third connecting portions are first removed bysubjecting the substrate with the semiconductor layer to an etchingoperation, and then the second resist portions having the secondthickness are removed by subjecting the first and second positive resistportions to an ashing operation, for example, so that the semiconductorlayers are formed into semiconductor elements..

According to a first preferred form of the process of the first aspectof the invention, the halftone exposing step is implemented by using ahalftone photomask having a fully light-transmitting area, asemi-light-transmitting area and a fully light-shielding area, such thatthe first positive resist portions having the first thickness are formedwith the fully light-shielding area of the halftone photomask preventingthe radiation from exposing the portions of the semiconductor layerwhich correspond to the thin-film transistor elements, and theresist-free areas are formed with the fully light-transmitting area ofthe halftone photomask permitting the radiation to expose the portionsof the semiconductor layer which correspond to the first, second andthird connecting portions of the semiconductor layer, while the secondpositive resist portions having the second thickness are formed with thesemi-light-transmitting area of the halftone photomask permittingpartial exposure of the other portions of the semiconductor layer to theradiation.

According to a second preferred form of the process of the first aspectof the invention, the halftone exposing step is implemented by using aphotomask having a fully light-transmitting area and a fullylight-shielding area, while the photoresist on the semiconductor layeris exposed through the photomask to a ultraviolet radiation whoseirradiation energy density is determined so as to remove only a portionof a thickness of the photoresist, the halftone exposing step beingimplemented such that the first positive resist portions having thefirst thickness are formed with the fully light-shielding area of thephotomask preventing the ultraviolet radiation from exposing theportions of the semiconductor layer which correspond to the thin-filmtransistor elements, while the second positive resist portions havingthe second thickness are formed with the fully light-transmitting areaof the photomask permitting the ultraviolet radiation to expose theabove-indicated other portions of the semiconductor layer, and whereinthe halftone exposing step further includes an operation performed afterthe first and second positive resist portions are formed, to form theresist-free areas by exposing portions of the photoresist exposed to theultraviolet radiation, which portions cover the portions of thesemiconductor layer corresponding to the first, second and thirdconnecting portions, such that the portions of the photoresist areexposed to a radiation through another photomask different from thephotomask used to form the first and second positive resist portions, orto respective spot lights of a condensed ultraviolet radiation.

According to a third preferred form of the process of the first aspectof the invention, the halftone exposing step is implemented by using aphotomask having a fully light-transmitting area and a fullylight-shielding area, while the photoresist on the semiconductor layeris exposed through the photomask to a ultraviolet radiation whoseirradiation energy density is determined so as to remove only a portionof a thickness of the photoresist, the halftone exposing step beingimplemented such that the first positive resist portions having thefirst thickness are formed with the fully light-shielding area of thephotomask preventing the ultraviolet radiation from exposing theportions of the semiconductor layer which correspond to the thin-filmtransistor elements, and the second positive resist portions having thesecond thickness are formed with the fully light-transmitting area ofthe photomask permitting the ultraviolet radiation to expose theabove-indicated other portions of the semiconductor layer, while at thesame time the resist-free areas are formed by exposing portions of thephotoresist covering the portions of the semiconductor layercorresponding to the first, second and third connecting portions, torespective spot lights of a condensed ultraviolet radiation.

The second object described above may be achieved according to a secondaspect of the present invention, which provides a liquid crystal displaydevice of transverse electric-field type manufactured by a processaccording to the first aspect of the invention described above.

According to one preferred form of the liquid crystal display oftransverse electric-field type of the second aspect of the invention,the first and second connecting portions have widths which are about ½to about 1/100 of that of the third connecting portion.

The third object may be achieved according to a third aspect of thisinvention, which provides a scan-exposing device used in a process ofmanufacturing a liquid crystal display device of transverseelectric-field type according to the first aspect of the invention, thescan-exposing device comprising:

a film-thickness measuring device operable to measure an actual value ofthe second thickness of the second positive resist portions formed inthe halftone exposing step; and

a feedback control device operable to feedback-control an amount ofexposure of the photoresist to the radiation, depending upon the actualvalue of the second thickness of the second positive resist portionsmeasured by the film-thickness measuring device.

The third object may also be achieved according to a fourth aspect ofthis invention, which provides a scan-exposing device used in a processof manufacturing a liquid crystal display device of transverseelectric-field type according to the first aspect of this invention, thescan-exposing device comprising:

a white light interferometer operable to measure at least one of (a) adifference between actual values of the first and second thicknesses ofthe first and second positive resist portions formed in the halftoneexposing step, and (b) the actual value of the second thickness of thesecond positive resist portions with respect to the resist-free areas;and

a feedback control device operable to feedback-control an amount ofexposure of the photoresist to the radiation, depending upon theabove-indicated at least one of the difference and the actual value ofthe second thickness which has been measured by the white lightinterferometer.

The third object described above may also be achieved according to afifth aspect of this invention, which provides a scan-exposing deviceused in a process of manufacturing a liquid crystal display deviceincluding a pair of substrates at least one of which is transparent, anda layer of a liquid crystal composition interposed between the pair ofsubstrates, the scan-exposing device being operable to scan-expose aphotoresist applied to one of the pair of substrates, to a ultravioletradiation through a quartz photomask substrate having a desiredlight-shielding pattern, the scan-exposing device comprising:

at least one Bernoulli chuck of non-contact type disposed so as to beopposed to one of opposite surfaces of the above-indicated one substrateupon which the ultraviolet radiation is incident, the above-indicated atleast one Bernoulli chuck being operable to reduce an amount ofdeflection of the quartz photomask substrate due to its own weight whilethe quartz photomask substrate is placed in a horizontally extendingposition;

a laser displacement meter operable to measure an amount of displacementof the above-indicated one of opposite surfaces of the quartz photomasksubstrate in a vertical direction; and

a substrate-position control device operable to control the at least oneBernoulli chuck on the basis of the amount of vertical displacementmeasured by the laser displacement meter, while the photoresist isscan-exposed to the ultraviolet radiation through the quartz photomasksubstrate.

The second object may also be achieved according to a sixth aspect ofthe invention, which provides a liquid crystal display device oftransverse electric-field type manufactured by using a scan-exposingdevice according to the fifth aspect of the invention described above.

The third object may also be achieved according to a seventh aspect ofthis invention, which provides a scan-exposing device used in a processof manufacturing a liquid crystal display device including a pair ofsubstrates at least one of which is transparent, and a layer of a liquidcrystal composition interposed between the pair of substrates, thescan-exposing device being operable to scan-expose a photoresist appliedto one of the pair of substrates, through a quartz photomask substratehaving a desired light-shielding pattern, the scan-exposing devicecomprising:

a quartz substrate disposed in opposition to the quartz photomasksubstrate and cooperating with the quartz photomask substrate to definetherebetween an air-tight space;

a pressure sensor operable to detect a pressure within the air-tightspace; and

a pressure control device operable to control a difference between thepressure within the air-tight space measured by the pressure sensor andan atmospheric pressure such that the pressure within the air-tightspace is lower than the atmospheric pressure by the difference so as toreduce an amount of deflection of the quartz photomask substrate due toits own weight, while the photoresist is scan-exposed through the quartzphotomask substrate.

The second object may also be achieved according to an eighth aspect ofthe invention, which provides a liquid crystal display device oftransverse electric-field type manufactured by using a scan-exposingdevice according to the seventh aspect of the invention described above.

The third object may also be achieved according to a ninth aspect of theinvention, which provides a scan-exposing device used in a process ofmanufacturing a liquid crystal display device including a pair ofsubstrates at least one of which is transparent, and a layer of a liquidcrystal composition interposed between the pair of substrates, thescan-exposing device being operable to scan-expose a photoresist appliedto one of the pair of substrates, through a photomask having a desiredlight-shielding pattern, the scan-exposing device comprising:

a slide carrying the above-indicated one of the pair of substrates;

photomask scan-exposing means for scan-exposing the photoresist whilethe photomask and the slide are moved at a same speed in a samedirection; and

spot scan-exposing means for directly spot scan-exposing the photoresistwithout using the photomask, with a spot size ranging from about 0.1 mmto about 5 mm,

and wherein the photomask scan-exposing means and the spot scan-exposingmeans are operable concurrently to expose the photoresist.

The second object may also be achieved according to a tenth aspect ofthe invention, which provides a liquid crystal display devicemanufactured by using a scan-exposing device according to the ninthaspect of this invention described above.

According to one preferred form of the scan-exposing device of the ninthaspect of the invention, the photomask scan-exposing means is operableto expose the photoresist through the photomask to a ultravioletradiation whose irradiation energy density is determined so as to removeonly a portion of a thickness of the photoresist, and the spotscan-exposing means includes a spot scan-exposing optical systemoperable to expose the photoresist to a spot light of a condensedultraviolet radiation, and wherein the photomask scan-exposing means andthe spot scan-exposing means are operable in one of two modes:consisting of: a mode in which the spot scan-exposing means is operatedafter an operation of the photomask scan-exposing means; and a mode inwhich the spot scan-exposing means is operated to expose the photoresistin a direct direction while the photomask scan-exposing means isoperated to expose the photoresist in the first direction, and the spotscan-exposing means is operated to expose the photoresist in a seconddirection perpendicular to the first direction after a photomask scanexposure of the photoresist by the photomask scan-exposing means iscompleted over an entire surface areas of the photoresist.

The first object indicated above may also be achieved according to aneleventh aspect of this invention, which provides a process ofmanufacturing a liquid crystal display device of transverseelectric-field type including (a) a pair of substrates at least one ofwhich is transparent, (b) a layer of a liquid crystal compositioninterposed between the pair of substrates, (c) a plurality of scanninglines driven by an external scanning-line driver circuit throughscanning-line terminal portions and extending in a line direction, (d) aplurality of image-signal wires extending in a column direction, (e)picture-element electrodes corresponding to respective picture elements,(f) common electrodes cooperating with the picture-element electrodes,and (g) thin-film transistor elements connected to the scanning linesand the image-signal wires, and wherein the scanning lines, theimage-signal wires, the picture-element electrodes, the commonelectrodes and the thin-film transistor elements are provided on asurface of one of the pair of substrates which faces the layer of theliquid crystal composition, the process comprising:

a first photomasking step of forming a positive resist that coversportions of a semiconductor layer formed on the one substrate, whichportions correspond to gate electrodes of the thin-film transistorelements and the common electrodes;

a second photomasking step of forming a positive resist that coversportions of the semiconductor layer which correspond to the thin-filmsemiconductor elements, and forming resist-free areas that coverportions of the semiconductor layer which correspond to a firstconnecting portion, a second connecting portion and a third connectingportion, the first connecting portion being provided to form firststatic-electricity protective transistor elements connecting the commonelectrodes and the scanning lines, the second connecting portion beingprovided to form second static-electricity protective transistorelements connecting the common electrodes and the image-signal wires,and the third connecting portion connecting the external scanning-linedriver circuit and the scanning line terminal portions;

a third photomasking step of forming a positive resist that coversportions of the semiconductor layer which correspond to sourceelectrodes and drain electrodes of the thin-film transistor elements,and the picture-elements electrodes; and

a fourth photomasking step of forming a positive resist for formingcontact holes of the scanning-line terminal portions and contact holesof image-signal wire terminal portions.

The first object may also be achieved according to a twelfth aspect ofthe invention, which provides a process of manufacturing a liquidcrystal display device of transverse electric-field type including (a) apair of substrates at least one of which is transparent, (b) a layer ofa liquid crystal composition interposed between the pair of substrates,(c) a plurality of scanning lines driven by an external scanning-linedriver circuit through scanning-line terminal portions and extending ina line direction, (d) a plurality of image-signal wires extending in acolumn direction, (e) picture-element electrodes corresponding torespective picture elements, (f) common electrodes cooperating with thepicture-element electrodes, and (g) thin-film transistor elementsconnected to the scanning lines and the image-signal wires, and whereinthe scanning lines, the image-signal wires, the picture-elementelectrodes, the common electrodes and the thin-film transistor elementsare provided on a surface of one of the pair of substrates which facesthe layer of the liquid crystal composition, the process beingcharacterized by comprising:

a first photomasking step of forming a positive resist that coversportions of a semiconductor layer formed on the one substrate, whichportions correspond to gate electrodes of the thin-film transistorelements and the common electrodes;

a second photomasking step of forming a positive resist that coversportions of the semiconductor layer which correspond to the thin-filmsemiconductor elements, and forming resist-free areas that coverportions of the semiconductor layer which correspond to a firstconnecting portion, a second connecting portion and a third connectingportion, the first connecting portion being provided to form firststatic-electricity protective transistor elements connecting the commonelectrodes and the scanning lines, the second connecting portion beingprovided to form second static-electricity protective transistorelements connecting the common electrodes and the image-signal wires,and the third connecting portion connecting the external scanning-linedriver circuit and the scanning line terminal portions;

a third photomasking step of forming a positive resist that coversportions of the semiconductor layer which correspond to sourceelectrodes and drain electrodes of the thin-film transistor elements,and the picture-elements electrodes; and

a passivation step of subjecting a back channel portion of each of thethin-film transistor elements to a plasma doping treatment with a B₂H₆gas, and coating the back channel portion with a layer formed of one ofBCB, polyphenyl silazane and an organic material by ink-jet coating orflexo graphic printing method.

While the concept of the present invention is similar to that disclosedin the above-identified publication JP-A-2000-066240 in that both ofthese concepts utilize the halftone exposure technique to reduce therequired number of the photomask. However, the portions of thesemiconductor layer on which the second positive resist portions havingthe second thickness smaller than the first thickness are formedaccording to the present invention are different from those according tothe technique in JP-A-2000-066240.

In the process of manufacturing a liquid crystal display of transverseelectric-field type according to the first aspect of the inventiondescribed above, the use of a single photomask permits removal of localportions of the semiconductor layer, so as to form the thin-filmtransistor elements, and formation of the first, second and thirdconnecting portions on the substrate in question. Thus, the presentprocess makes it possible to reduce the required number of photomasks,leading to an accordingly reduced cost of manufacture of the liquidcrystal display device of transverse electric-field type. Further, thethin-film transistor elements of the display device manufactured in thepresent process has substantially no variation in the length of thechannel portions of the thin-film transistor elements, which lengthdetermines the characteristic of the thin-film transistor elements.Accordingly, the present process permits mass production of the liquidcrystal display with high stability. Although the dimensional accuracyof the thin-film transistor elements formed by removal of the localportion of the semiconductor layer according to the present process ismore or less lower than that of the thin-film transistor elements formedin the process disclosed in JP-A-2000-066240, a variation in thisdimensional accuracy will cause substantially no variation in thecharacteristic of the thin-film transistor elements, provided thesemiconductor layer has a width dimension larger than that of the gateelectrodes. The present process tends to suffer from a lower degree ofdimensional accuracy of the first connecting portion provided to formthe first static-electricity protective transistor elements connectingthe common electrodes and the scanning lines, the second connectingportion provided to form the second static-electricity protectivetransistor elements connecting the common electrodes and theimage-signal wires, and the third connecting portion connecting theexternal scanning-line driver circuit and the scanning-line terminalportions, than in the process disclosed in JPA-2000-066240. However, avariation in the dimensional accuracy of the first, second and thirdconnecting portions has substantially no adverse influence on thecharacteristic of the thin-film transistor elements.

In the process according to the second or third preferred form of theprocess of the first aspect of the invention described above, thehalftone exposing step can be implemented without using a specialphotomask as used in the process disclosed in JP-A-2000-066240. Whilethe conventional mass production of the liquid crystal display deviceusing the halftone exposure requires the use of a photomask having ahigh degree of dimensional accuracy, the process according to the secondor third preferred form of the process of the invention does not requirethe use of such a photomask to implement the halftone exposure, andtherefore increases the freedom in the design of the photomask to beused, resulting in a considerable reduction in the cost of manufactureof the photomask.

In the process according to the third preferred form of the process ofthe first aspect of the invention described above, the first positiveresist portions having the first thickness are formed with the fullylight-shielding area of the photomask preventing the ultravioletradiation from exposing the portions of the semiconductor layer whichcorrespond to the thin-film transistor elements, and the second positiveresist portions having the second thickness smaller than the firstthickness are formed with the fully light-transmitting area of thephotomask permitting the ultraviolet radiation to expose the otherportions of the semiconductor layer, while at the same time theresist-free areas are formed by exposing portions of the photoresistcovering the portions of the semiconductor layer corresponding to thefirst, second and third connecting portions, to the respective spotlights of the condensed ultraviolet radiation. This process permitsefficient formation of the first and second positive resist portionshaving the respective first and second thickness values and theresist-free areas, resulting in a significant improvement in theefficiency of manufacture of the liquid crystal display device.

The liquid crystal display device of transverse electric-field typeaccording to the second aspect of this invention described above ismanufactured by the process according to the first aspect of theinvention, which requires the use of a single photomask as describedabove. Accordingly, the present liquid crystal display device isavailable at a relatively low cost.

In the preferred form of the second aspect of the invention describedabove, the width of the third connecting portion is made larger thanthose of the first and second connecting portions, so that the contactresistance at the third connecting portion connecting the externalscanning-line driver circuit and the scanning-line terminal portions canbe lowered to minimize a variation in the horizontal stripes on thescreen of the display device.

In the scan-exposing device according to the third aspect of thisinvention described above, the film-thickness measuring device isprovided to measure the actual value of the second thickness of thesecond positive resist portions formed in the halftone exposing step,and the amount of exposure of the photoresist to the radiation isfeedback-controlled by the feedback control device, depending upon theactual value of the second thickness of the second positive resistportions measured by the film-thickness measuring device. In the processof manufacturing a liquid crystal display device of transverseelectric-field type according to the first aspect of this invention, thepresent scan-exposing device permits easy formation of the first andsecond positive resist portions having the different first and secondthickness values, while minimizing a variation in the thickness valueswhich would otherwise be inherent to the halftone exposing sep, so thatthe liquid crystal display device can be mass-produced with a highdegree of stability. Where the scan-exposing device is of amultiple-lens projection exposing type as shown in FIGS. 17 and 18 andas described below, the amount of exposure of the photoresist to aultraviolet radiation can be easily adjusted owing to a bundle of quartzfibers extending from a light source. In the halftone exposing step, theuniformity of the amount of exposure of the photoresist to theultraviolet radiation is particularly important. A variation in thethickness of the positive resist portions which have beenhalftone-exposed and developed prevents mass production of the liquidcrystal display device. In this respect, the yield ratio of the displaydevice is appreciably improved by controlling the distribution andamount of exposure of the photoresist to the ultraviolet radiation foreach of the substrates on the basis of the actual values of thethicknesses of the positive resist portions accurately measured by thefilm-thickness measuring device.

In the scan-exposing device according to the fourth aspect of theinvention described above, the white light interferometer is provided tomeasure at least one of the difference between the actual values of thefirst and second thicknesses of the first and second positive resistportions formed in the halftone exposing step, and the actual value ofthe second thickness of the second positive resist portions with respectto the resist-free areas. The amount of exposure of the photoresist tothe radiation is feedback-controlled by the feedback control device,depending upon the above-indicated difference and/or the actual value ofthe second thickness which has been measured by the white lightinterferometer. In the process of manufacturing a liquid crystal displaydevice of transverse electric-field type according to the first aspectof this invention, the present scan-exposing device permits easyformation of the first and second positive resist portions having thedifferent first and second thickness values, while minimizing avariation in the, thickness values which would otherwise be inherent tothe halftone exposing sep, so that the liquid crystal display device canbe mass-produced with a high degree of stability. Where thescan-exposing device is of a multiple-lens projection exposing type asshown in FIGS. 17 and 18 and as described below, the amount of exposureof the photoresist to a ultraviolet radiation can be easily adjustedowing to a bundle of quartz fibers extending from a light source. In thehalftone exposing step, the uniformity of the amount of exposure of thephotoresist to the ultraviolet radiation is particularly important. Avariation in the thickness of the positive resist portions which havebeen halftone-exposed and developed prevents mass production of theliquid crystal display device. In this respect, the yield ratio of thedisplay device is appreciably improved by controlling the distributionand amount of exposure of the photoresist to the ultraviolet radiationfor each of the substrates on the basis of the actual values of thethicknesses of the positive resist portions accurately measured by thewhite light interferometer.

In the scan-exposing device according to the fifth aspect of theinvention described above, the quartz photomask substrate has thedesired light-shielding pattern, and the at least one Bernoulli chuck ofnon-contact type is disposed so as to be opposed to one of oppositesurfaces of the above-indicated one substrate upon which the ultravioletradiation is incident. The at least one Bernoulli chuck is operable toreduce the amount of deflection of the quartz photomask substrate due toits own weight while the quartz photomask substrate is placed in thehorizontally extending position. Further, the laser displacement meteris provided to measure the amount of displacement of the above-indicatedone of opposite surfaces of the quartz photomask substrate in a verticaldirection. While the photoresist on the substrate in question isscan-exposed to the ultraviolet radiation through the quartz photomasksubstrate, the at least one Bernoulli chuck is controlled by thesubstrate-position control device, on the basis of the amount ofvertical displacement measured by the laser displacement meter. Thus,the present scan-exposing device permits scan-exposure of thephotoresist while the quartz photomask substrate is held substantiallyflat extending in the horizontal direction, with the amount ofdeflection of the quartz photomask substrate being reduced by the atleast one Bernoulli chuck. Where the quartz photomask substrate islarge-sized, the photoresist scan-exposed by the conventionalscan-exposing device undesirably has under-focused and over-focusedlocal portions due to a relatively large amount of deflection of thequartz photomask substrate cased by its own weight, resulting in a lowdegree of uniformity of resolution of exposure and development of thephotoresist. To the contrary, the scan-exposing device according to thepresent fifth aspect of the invention assures a significant improvementin the uniformity of resolution in the exposure and development of thephotoresist. While two or more quartz photomask substrates of arelatively small size may be jointed into a single large-sized quartzphotomask substrate to be used for the exposure, this approach suffersfrom a problem caused visible junctions between the small-sizedsubstrates, and a problem of difficulty to design the junctions. Thescan-exposing device according to the present fifth aspect of theinvention makes it possible to achieve the san exposure by using asingle quartz photomask substrate.

The liquid crystal display device of transverse electric-field typeaccording to the sixth aspect of the invention described above ismanufactured by using the scan-exposing device according to the fifthaspect of the invention, which permits easy scan exposure of thephotoresist using a large-sized quartz photomask substrate, and assuresan accordingly reduced cost of manufacture of the liquid crystal displaydevice. The present liquid crystal display device has a high degree ofuniformity in its resolution, since the scan-exposing device used tomanufacture the display device is effective to minimize theunder-focused and over-focused portions of the photoresist, which wouldreduce the uniformity in the resolution.

In the scan-exposing device according to the seventh aspect of theinvention described above, the quartz substrate disposed in oppositionto the quartz photomask substrate having the desired light-shieldingpatter, such that the quartz substrate cooperates with the quartzphotomask substrate to define therebetween an air-tight space, and thepressure sensor is provided to detect a pressure within the air-tightspace. The difference between the pressure within the air-tight spaceand an atmospheric pressure is controlled by the pressure control devicesuch that the pressure within the air-tight space is lower than theatmospheric pressure by the controlled difference so as to reduce theamount of deflection of the quartz photomask substrate due to its ownweight, while the photoresist is scan-exposed through the quartzphotomask substrate. The present scan-exposing device permits easy scanexposure of the photoresist by using a single large-sized quartzphotomask substrate, and makes it possible to minimize the deteriorationof the uniformity in the resolution of patterning of the photoresist dueto the under-focused and over-focused portions.

The liquid crystal display device of transverse electric-field typeaccording to the eighth aspect of the invention described above ismanufactured by using the scan-exposing device according to the seventhaspect of the invention, which permits easy scan exposure of thephotoresist using a large-sized quartz photomask substrate, and assuresan accordingly reduced cost of manufacture of the liquid crystal displaydevice. The present liquid crystal display device has a high degree ofuniformity in its resolution, since the scan-exposing device used tomanufacture the display device is effective to minimize theunder-focused and over-focused portions of the photoresist, which wouldreduce the uniformity in the resolution.

The scan-exposing device according to the ninth aspect of this inventiondescribed above is used in a process of manufacturing a liquid crystaldisplay device including a pair of substrates at least one of which istransparent, and a layer of a liquid crystal composition interposedbetween the pair of substrates. This scan-exposing device includes theslide carrying the above-indicated one of the pair of substrates, thephotomask scan-exposing means for scan-exposing the photoresist whilethe photomask and the slide are moved at a same speed in a samedirection, and the spot scan-exposing means for directly spotscan-exposing the photoresist without using the photomask, with a spotsize ranging from about 0.1 mm to about 5 mm. In the presentscan-exposing device, the photomask scan-exposing means and the spotscan-exposing means are operable concurrently to expose the photoresist.The present scan-exposing device permits simultaneous formation of firstresist portions having a first thickness, second resist portions havinga second thickness, and resist-free areas, by scan-exposing thephotoresist, thereby significantly improving the efficiency ofmanufacture of the liquid crystal display device. Since thescan-exposing device incorporates both of the photomask scan-exposingmeans and the spot scan-exposing means, the required number of exposingdevices can be reduced, making it possible to reduce the required areaof a clean room accommodating the exposing devices, leading to aconsiderable increase in the efficiency of investment.

The liquid crystal display device of transverse electric-field typeaccording to the tenth aspect of the invention described above ismanufactured by using the scan-exposing device according to the ninthaspect of the invention, which permits efficient and economicalmanufacture of the liquid crystal display device.

In the scan-exposing device according to the preferred form of the ninthaspect of the invention described above, the photoresist is firstexposed by the photomask scan-exposing means using the photomask and theultraviolet radiation whose irradiation energy density is reduced, andis then exposed by the spot scan-exposing means. The photomask scanexposure of the photoresist by the photomask scan-exposing meansrequires the photoresist patterning resolution of about 3 μm-10 μm,while the spot scan exposure by the spot scan-exposing means requiresthe resolution of as low as about 100 μm. Therefore, the yield ratio ofthe liquid crystal display device can be improved by implementing thephotomask scan exposure requiring the higher photoresist patterningresolution, before dust is deposited on the substrate (glass substrate)carrying the photoresist, namely, before the spot scan exposure, andthen implementing the spot scan exposure by the spot scan-exposingmeans, in which the dust does not have a significant influence on thepatterning of the photoresist.

In the process of manufacturing the liquid crystal display deviceaccording to the eleventh aspect of the present invention describedabove, the manufacture of the liquid crystal display device oftransverse electric-field type requires only four photomasking steps,and a relatively small number of photomasks. Accordingly, the presentprocess permits economical manufacture of the liquid crystal displaydevice.

In the process of manufacturing the liquid crystal display deviceaccording to the twelfth aspect of this invention described above, themanufacture of the liquid crystal display device of transverseelectric-field type requires only three photomasking steps, and arelatively small number of photomasks. Accordingly, the present processpermits economical manufacture of the liquid crystal display device.

The process according to the eleventh or twelfth aspect of the inventionpermits economical manufacture of the liquid crystal display device ofactive matrix type with a high yield ratio, and with a high degree ofconsistency in the characteristic of the thin-film transistor elements.In addition, static-electricity protective circuits for protectingactive matrix elements against static electricity generated in theprocess of manufacture of the liquid crystal display device can beincorporated within the interior of the active matrix substrate, so thatthe process of manufacture can be easily controlled so as to minimize arisk of defects of the display device.

The process according to the first aspect, eleventh aspect or twelfthaspect of the invention permits manufacture of the liquid crystaldisplay device, without using transparent conductive films. Further, thepresent process permits the use of metallic materials, metal silicidecompounds or metal nitride, as the materials of the electrodes, so thatthe cost of sputtering targets for the electrodes can be reduced.Similarly, all of the static-electricity protective transistor circuitsformed on the active matrix substrate may be formed of metallicmaterials, metal silicide compounds or metal nitride, a relatively largeamount of electric current can be applied to the static-electricityprotective transistor circuits. This aspect is particularly important inthe process of manufacture of a liquid crystal display device of a40-inch or larger size. Namely, the production line for the displaydevice is not required to comply with a static electricity protectionstandard which is severer than the conventional standard, so that thefeeding speed of the substrate need not be reduced. An increase in thefeeding speed of the substrate permits an accordingly improvedefficiency of manufacture and an increased yield ratio of the displaydevice.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, advantages and technical andindustrial significance of the present invention will be betterunderstood by reading the following detailed description of presentlypreferred embodiments of the invention, when considered in connectionwith the accompanying drawings, in which:

FIG. 1 is an elevational view in cross section showing a halftonephotomask and a photoresist layer after development, in the prior art;

FIG. 2 is an elevational view in cross section showing a halftonephotomask and a photoresist layer after development, according to afirst embodiment of the present invention;

FIG. 3 is a flow chart illustrating a photomasking process according tothe first embodiment;

FIG. 4 is a flow chart illustrating a photomasking process according toa second embodiment of the present invention;

FIG. 5 is a circuit diagram depicting a static-electricity protectivetransistor element according to the present invention;

FIG. 6 is a circuit diagram depicting a static-electricity protectivetransistor element according to the invention;

FIG. 7 is a plan view of a static-electricity protective transistorelement according to the present invention;

FIG. 8 is a plan view of a static-electricity protective transistorelement according to the present invention;

FIG. 9 is a plan view of a static-electricity protective transistorelement according to the present invention;

FIG. 10 is a plan view of a static-electricity protective transistorelement according to the present invention;

FIG. 11A through FIG. 11F are elevational views in cross section of anactive matrix substrate, explaining a halftone exposing step accordingto the first embodiment;

FIGS. 12A, 12B and 12C are elevational views in cross section showing acombination exposure process and a photoresist layer after thedevelopment, according to a second embodiment of the invention

FIG. 13 is a plan view of a static-electricity protective transistorelement formed in the combination exposing step according to the secondembodiment;

FIG. 14 is a plan view of a static-electricity protective transistorelement also formed according to the second embodiment;

FIG. 15A through FIG. 15E are elevational views in cross section of anactive matrix substrate, explaining the halftone exposing step accordingto the second embodiment;

FIG. 16 is a plan view of an active matrix substrate of transverseelectric-field type produced in the halftone exposing step according tothe second embodiment;

FIG. 17 is a plan view of a scan-exposing device used to effect ahalftone exposing step according to a third embodiment of the presentinvention;

FIG. 18 is a plan view of a scan-exposing device used to effect ahalftone exposing step according to a fourth embodiment of theinvention;

FIG. 19 is a flow chart illustrating a feedback control used to effectthe halftone exposing step of the present invention;

FIG. 20 is a view showing an optical principle of a white lightinterferometer used according to the present invention, for measuringsteps between positive resists having a first and a second thickness andan areas not coated with a positive resist;

FIG. 21 is a plane view of an active matrix substrate of transverseelectric-field type produced in the halftone exposing step according tothe second embodiment;

FIG. 22 is a flow chart illustrating a photomasking process utilizing aconventional halftone exposing step;

FIG. 23 is an elevational view in cross section showing a scan-exposingdevice used to effect a halftone exposing step according to a fifthembodiment of the present invention; and

FIG. 24 is an elevational view in cross section of a scan-exposing stepused to effect a halftone exposing step according to a sixth embodimentof the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of this invention will be described. In the firstembodiment, a halftone photomask 60 as shown in the cross sectional viewof FIG. 1 is used in a halftone exposing step. The halftone photomask 60includes a photomask substrate 1 (quartz glass), and a photomask metal62 and a semi-light-transmitting portion 64 which are formed on thesubstrate 1. The photomask metal 62 provides the halftone photomask 60with a fully light-shielding area (fully light-blocking area), while aportion of the semi-light-transmitting portion 64 which is not held incontact with the photomask metal 62 provides the halftone photomask 60with a semi-light-transmitting area. The halftone photomask 60 has afully light-transmitting area 65 in which the semi-light-transmittingportion 64 is not formed.

There will next be described the halftone exposing step. FIGS. 11Athrough 11B are cross sectional views of an active matrix substrate, forexplaining the halftone exposing step. FIG. 11A shows a resist patternformed on the active matrix substrate 9, by using the halftone photomask60 described above. This resist pattern includes a positive resistportion 6 which has a predetermined first thickness and which isprevented by the fully light-shielding area of the halftone photomask 60from being exposed to a ultraviolet radiation. This positive resistportion 6 covers a portion of the active matrix substrate 9 at which athin-film transistor element 58 is formed so as to be superposed on agate electrode 55. The resist pattern further has a resist-free area 8which is not provided with any positive resist portion and whichcorresponds to the fully light-transmitting area 65 of the halftonephotomask 60 that permits full transmission of the ultraviolet radiationtherethrough. This resist-free area 8 covers a portion of the activematrix substrate 9 at which there is formed a third connecting portionin the form of a contact hole 59 which connects an externalscanning-line driver circuit (not shown) and a scanning-line terminalportion 19 through a junction electrode 21. The resist pattern formed inthe step shown in FIG. 11A further has other resist-free areas coveringa first connecting portion and a connecting portion in the form ofcontact holes 18 (shown in FIG. 7) for forming static-electricityprotective transistor elements 42 (shown in FIG. 7). As also shown inFIG. 11A, the resist pattern further includes a positive resist portion7 which has a second thickness smaller than the first thickness of thepositive resist portion 6 and which is the portion other than thepositive resist portion 6 and the resist-free area 8.

Then, the active matrix substrate 9 is subjected to an etchingoperation, so as to remove portions of semiconductor layers 10, 11, abarrier metal layer 12 and a low-resistance metal layer 13, whichportions correspond to the resist-free area 8 of the resist pattern. Asa result, the contact hole 59 is formed. Subsequently, the resistpattern is entirely subjected to an ashing operation, for example, toremove the positive resist portion 7 having the second thickness. FIG.11B shows the active matrix substrate 9 after the etching and ashingoperations.

Then, the substrate 9 is subjected to an etching operation, to removeportions of the semiconductor layers 10, 11, barrier metal layer 12 andlow-resistance metal layer 13, which portions are not covered by thepositive resist portion 6. As a result, the portions of thesemiconductor layers 10, 11 which are left are formed into semiconductorelements. FIG. 11C shows the step in which the semiconductor layers 10,11 on the active matrix substrate 9 are formed into the semiconductorelements.

Referring next to the flow chart of FIG. 3, there is illustrated aphotomasking process performed in a process of manufacturing a liquidcrystal display device of transverse electric-field type according tothe first embodiment of the invention. In a first photomasking step 140,a positive resist is first formed on portions of the substrate 9 whichcorrespond to the gate electrode 55 and a common electrode 20. In asecond photomasking step 141, the positive resist portion 6 is formed ona portion of the substrate 9 corresponding to the thin-film transistorelement 58, and the resist-free area 8 are formed on portions of thesubstrate 9 which correspond to the contact holes 18, 59, while thepositive resist portion 7 is formed on the other portion of thesubstrate 9. The second photomasking step 141 is a halftone exposingstep according to the present invention. In a third photomasking step142, a positive resist is formed on portions of the substrate 9 whichcorrespond to a source electrode 54, a drain electrode 56 and apicture-element electrode 22. In a fourth photomasking step 143, apositive resist is formed for forming a contact hole 24 at thescanning-line terminal portion 19 shown in FIG. 11F, and contact holesat image-signal-wire terminal portions 34 (FIG. 16).

Referring to the circuit diagrams of FIGS. 5 and 6, there are showncircuits of the static-electricity protective transistor elements 42used in the present invention. However, these circuits may be replacedby any other circuits, depending upon the desired function of thecircuits. The plan views of FIGS. 7-10 show the circuits of thestatic-electricity protective transistor elements 42 formed in theprocess of the invention.

In the conventional halftone exposing step disclosed in JP-A-2000-066240uses the slit type photomask 70 as shown in FIG. 1. The slit typephotomask 70 has a photomask metal 72, and a slit area having slits 73which are formed so as to reduce the average amount of transmission ofultraviolet radiation through the slit area, so that a portion of thesubstrate 9 at which the channel portion of the thin-film transistorelement is to be formed is provided with a positive resist portionhaving a smaller thickness than a positive resist portion formed at aportion of the substrate 9 which corresponds to the photomask metal 72.Thus, the use of the single photomask 70 permits formation of thesemiconductor layers 10, 11 into semiconductor elements, and formationof the channel portion of the thin-film transistor element. In the priorart disclosed in JPA-2000-066240, the active matrix substrate 9 ismanufactured in a photomasking process illustrated in the flow chart ofFIG. 22. However, the conventional photomasking process according toJP-A-2000-066240 suffers from a low degree of accuracy in the length ofthe channel portion, giving rise to a problem of a relatively largeamount of variation in the characteristic of the thin-film transistorelement.

Unlike the technique disclosed in JP-A-2000-066240, the processaccording to the present embodiment is not formulated to form thechannel portion of the thin-film transistor element in the halftoneexposing step. In the present first embodiment, the channel portion 57of the thin-film transistor element 58 is formed in the step of FIG.11D, only after the semiconductor layers 10, 11 are formed into thesemiconductor elements in the step of FIG. 11C. Therefore, the presentprocess suffers from substantially no variation in the length of thechannel portion 57 of the thin-film transistor element 58, and anextremely small amount of variation in the surface area at the portionof overlapping of the gate electrode 55, source electrode 54 and drainelectrode 56. Accordingly, the present process makes it possible tominimize the amount of variation in the characteristic of the thin-filmtransistor element 58, assuring stable mass production of a productincluding the thin-film transistor element 58.

In the present first embodiment illustrated in FIGS. 11A-11F, the activematrix substrate 9 can be manufactured by using metallic materials forforming two kinds of electrodes for the scanning lines and theimage-signal wires, so that the cost of manufacture of the substrate 9can be reduced. Although the substrate 9 subjected to the halftoneexposing step may have a variation in its dimensional accuracy, thisvariation which may occur in the first embodiment does not have anadverse influence on the characteristic of the thin-film transistorelement, making it possible to prevent reduction in the yield ratio of aliquid crystal display device manufactured in the present process, evenif the display device has a large-sized screen. Further, the commonelectrode 20 and the picture-element electrode 22 are entirely coveredby a passivation film 23, as shown in FIG. 11E, making it possible tominimize generation of an after-image phenomenon.

There will be described a second embodiment of this invention. Aspectsof the second embodiment which are similar to those of the firstembodiment will not be described. The plan views of FIGS. 16 and 21 showactive matrix substrates of transverse electric-field type manufacturedby a process of manufacture according to the present second embodiment.The second embodiment does not use the slit type photomask 70 shown inFIG. 1, or the halftone photomask 6 used in the first embodiment.

A halftone exposing step in the second embodiment will be described. Thecross sectional views of FIGS. 12A, 12B and 12C show the active matrixsubstrate 9, for explaining the halftone exposing step. The activematrix substrate 9 is exposed to a ultraviolet radiation 25 through aphotomask 80 shown in FIG. 12A. The photomask 80 includes a photomaskmetal 82 formed on the photomask substrate 1. The irradiation energydensity of the ultraviolet radiation 25 is lowered than in an ordinaryexposing step, so that only a portion of the thickness of a photoresistexposed to the ultraviolet radiation 25 is removed. The photomask metal82 which functions as a fully light-shielding area contains Cr or Mo,and the photomask substrate 1 has a fully light-transmitting area 85.FIG. 12A shows a non-exposed portion 26 of the photoresist whichcorresponds to the photomask metal 82, and an exposed portion 27 of thephotoresist which corresponds to the fully light-transmitting area 85.

In the next step shown in FIG. 12B, an area 29 of the exposed portion 27in which contact grooves 91, 92, 93 (which will be described byreference to FIGS. 13, 14 and 16) are to be formed is exposed to theultraviolet radiation 25 which has been condensed by spot scan-exposingmeans in the form of a UV condenser lens 28. As a result, the area 29 ofthe exposed portion 27 of the positive resist is removed, and thesubstrate 9 is provided with a resist-free area 32 for the contactgrooves 91-93, as shown in FIG. 12C and FIG. 15A.

FIG. 12C shows the positive resist 6 after the development following theexposure in the two steps shown in FIGS. 12A and 12B. These two steps,namely, overall photomask scan exposure of the substrate 9 to theultraviolet radiation whose irradiation energy density is lowered asdescribed above, and spot scan exposure of the area 29 to spot lights ofthe condensed ultraviolet radiation 25 may be implemented by respectivedifferent devices. However, the halftone exposing process may beimplemented by a single device such as scan-exposing devices 100, 110,120, 130, which will be described.

In the second embodiment described above, the ultraviolet radiation 25is condensed into a spot light for irradiating the area 29 of thepositive resist to form the resist-free area 32 of the substrate 9.However, another photomask other than the photomask 80 may be used toexpose the substrate 9, so as to form the resist-free area 32. In thiscase, the exposure must be conducted by using the two photomasks, sothat the required, exposure time is undesirably increased due to achange of the photomask. Nevertheless, this alternative exposure methodis suitable where the substrate 9 is provided with a large number ofcontact holes.

Where an active matrix substrate having a considerable length largerthan 40 inches is exposed, in particular, a single large one-piecephotomask must be used to expose such a large substrate, since it isdifficult to implement the halftone exposing step by using two or morephotomasks which are joined together. Namely, it is difficult tosuitable join the two or more photomasks into a mask assembly. Where thephotomask has a length of 40 inches or more, it takes a considerabletime to change the photomask, resulting in a considerable reduction inthe throughput. The throughput can be appreciably improved byimplementing a combination exposure process in which the photomaskexposure and the spot scan exposure may be effected independently ofeach other by a single device such as the scan-exposing devices 100,110, 120, 130, which incorporates means for effecting photomask scanexposure using a photomask, and means for effecting spot scan exposureusing condensed spot lights. It is also noted that the photomask scanexposure using the photomask as shown in FIG. 12A and the spot scanexposure shown in FIG. 12B may be effected concurrently, so as tomaximize the efficiency of the halftone exposing process in the secondembodiment.

The plan views of FIGS. 13 and 14 show the static-electricity protectivetransistor elements 42 formed by the combination exposure process. Thecontact groove 91 serving as the first connecting portion, and thecontact groove 92 serving as the second connecting portion are formed byspot scan-exposing means. The plan view of FIGS. 16 and 21 show activematrix substrates of transverse electric-field type manufactured by theprocess of the second embodiment. These substrates have astatic-electricity protective circuit 102 consisting of a singlestatic-electricity protective transistor element 42 or a plurality ofstatic-electricity protective transistor elements. The contact groove 93serving as the third connecting portion has a width L₃ larger thanwidths L₁ and L₂ of the first and second connecting portions, that is,the contact grooves 91 and 92 of the terminal portions of thestatic-electricity protective transistor elements 42. Namely, the widthsL1-L3 are determined so as to satisfy the following equation (1), whichis formulated to minimize the contact resistance of the terminalportions of the scanning lines, for preventing a variation in thehorizontal stripes on the screen of the display device.

L ₁ =L ₂=(1−x)x L ₃   (1)

wherein the value “x” is equal to or larger than 1/100, and is equal toor smaller than ½.

The cross sectional views of FIGS. 15A-15E show the active matrixsubstrate 9, for explaining three photomasking steps in the combinationexposure according to the second embodiment. As in the first embodiment,the channel portion 57 of the thin-film transistor element 58 is notformed in the halftone exposing step, so that the length of the channelportion 57 has substantially no variation, making it possible tominimize a display variation due to a variation in the characteristic ofthe thin-film transistor element 58.

After the halftone exposing step, the source electrode 54 and the drainelectrode 56 are formed, as shown in FIG. 15D, by removing by dryetching an n⁺ layer which is formed by doping an ohmic contact layer inthe form of the semiconductor layer 11 with phosphor.

Then, a passivation step in the second embodiment will be described. Inthe passivation step, the surface of the channel portion 57 is subjectedto a plasma doping treatment in a hydrogen or nitrogen atmospherecontaining a diborane (B₂H₆) gas, and the surface is then coated with atransparent flattening film 33 formed of BCB (benzocyclo butene) orpolyphenyl silazane, as shown in FIG. 15E, by ink-jet printing, flexibleprinting, or any other suitable printing method. The transparentflattening film 33 has a thickness ranging from about 0.2 μm (2000 A) toabout 0.6 μm (6000 A). This transparent flattening film 33 may bereplaced by a polyimide film, which is usually used as an orientationfilm coated on an active matrix substrate. In this case, the polyimidefilm functions not only as a flattening film but also as an orientationfilm.

If the passivation step described above were not implemented, that is,if the substrate were not subjected to “back channel doping” wherein thesurface of the channel portion 57 is subjected to the plasma dopingtreatment in the hydrogen or nitrogen gas containing the diborane (B₂H₆)gas, the thin-film transistor element 58 would not exhibit a high degreeof reliability for a long period of time. If the back channel dopingcannot be implemented for some reason or other, the contact groove maybe formed by first forming a silicone nitriding film having a thicknessfrom about 0.2 μm (2000 A) to about 0.4 μm (4000 A), by plasma CVD, thenapplying a positive resist to the thus formed film, subjecting only theterminal portions of the scanning-line terminal portion 19 and thestatic-electricity protective transistor elements 42 to a spotscan-exposing operation, and after the development, implementing a dryetching operation so as to form the contact groove.

Referring to the flow chart of FIG. 4, there is illustrated thephotomasking steps in the process of manufacture of a liquid crystaldisplay device of transverse electric-field type according to the secondembodiment of the invention. In a first photomasking step 150, apositive resist is applied to portions of the substrate 9 whichcorrespond to the gate electrode 55 and the common electrode 20. In asecond photomasking step 151, the positive resist portion 6 is formed ona portion of the substrate 9 which corresponds to the thin-filmtransistor element 58, and the resist-free area 32 is formed on portionsof the substrate 9 which correspond to the contact grooves 91, 92, 93,while a positive resist portion 30 is formed on the other portions ofthe substrate 9, as shown in FIG. 15A. The second photomasking step 151is the halftone exposing step in the second embodiment. In a thirdphotomasking step 152, a positive resist is applied to portions of thesubstrate 9 which correspond to the source electrode 54, drain electrode56 and picture-element electrode 22. In a passivation step 153, the backchannel portion of the thin-film transistor element 58 is subjected tothe plasma doping treatment using a B₂H₆ gas, and is then coated with alayer of BCB, polyphenyl silazane or an organic material by ink-jetcoating or flexo graphic printing method.

According to the second embodiment, the active matrix substrate 9 can bemanufactured by only three photomasking steps, making it possible toconsiderably reduce the required number of process steps.

There will next be described a third embodiment of this invention. Theplan view of FIG. 17 shows the scan-exposing device 100 used in thethird embodiment. The scan-exposing device 100 is a multiple-lens typescan-exposing device including: an XY slide 37 which is arranged to holda glass substrate and movable in the X-axis and Y-axis directions; aphotomask substrate 36 which is movable in the Y-axis direction only;and a projection optical system 39. The scan-exposing device 100includes a spot scan-exposing optical system in the form of stationaryspot scan-exposing modules 40, so that the spot scan exposure by thespot scan-exposing means using the spot scan-exposing modules 40 can beimplemented after the photomask scan exposure by the photomaskscan-exposing means using the photomask substrate 36. The spot scanexposure is effected with a spot size ranging from about 0.1 mm to about5 mm.

The scan-exposing device 110 shown in the plane view of FIG. 18 is usedin a fourth embodiment of this invention. This scan-exposing device 110includes a Y-axis slide 38 which is movable in the Y-axis directiononly, a projection optical system 39, and a spot scan-exposing opticalsystem in the form of a spot scan-exposing optical module 41 which ismovable in the X-axis only. In this scan-exposing device 110, the spotscan exposure using the spot scan-exposing optical module 41 is effectedin the Y-axis direction with a spot size ranging from about 0.1 mm toabout 5 mm, while the photomask scan exposure using the photomasksubstrate 36 is effected in the Y-axis direction. After the photomaskscan exposure in the Y-axis direction by the photomask scan-exposingmeans using the photomask substrate 36 is effected over the entiresurface of the substrate, the spot scan exposure by the spotscan-exposing means using the spot scan-exposing optical module 41 iseffected in the X-axis direction.

Where a 60-inch active matrix liquid crystal display device ismanufactured, there may arise an undesirable problem of deflection of aquartz photomask substrate due to its own weight. One consideredsolution to this problem of deflection of the photomask substrate is todispose the quartz photomask substrate so as to extend in thelongitudinal direction. Where the glass substrate is extremely large,the weight of the slide is accordingly large, and the slide cannot besmoothly moved.

The scan-exposing device 120 used in a fifth embodiment of the inventionis shown in the cross sectional view of FIG. 23. This scan-exposingdevice 120 includes: a UV source 43 which is operable to generate theultraviolet radiation and which is disposed on one of opposite sides ofthe quartz photomask substrate 36; non-contact type chucks in the formof Bernoulli chucks 45 which are disposed on the same side of the quartzphotomask substrate 36 and which are operable to control local verticalpositions of the photomask substrate 36, so as to reduce the amount ofdeflection of the substrate 36 due to its own weight; and red-laserdisplacement meters or gages 44 operable to measure a verticaldisplacement of the quartz photomask substrate 36, at its surface on theside of the Bernoulli chucks 45. The scan-exposing device 120 thusconstructed is capable of exposing a glass substrate 49 (active matrixsubstrate), while compensating for the deflection of the quartzphotomask substrate 36 due to its own weight, namely, while accuratelycontrolling the position of the substrate 36 as held by the Bernoullichucks 45, on the basis of the displacement measured by the red-laserdisplacement meters 44. To this end, a suitable substrate-positioncontrol device is provided to control the Bernoulli chucks 45 so as toreduce the amount of deflection of the quartz photomask substrate 36.Referring next to the cross sectional view of FIG. 24, there is shownthe scan-exposing device 130 used in a sixth embodiment of thisinvention, wherein a quartz substrate 76 is disposed in opposition tothe quartz photomask substrate 36 such that these substrates 76, 36cooperate to define therebetween an air-tight space. The scan-exposingdevice 130 is capable of exposing the glass substrate 49, whilecompensating for the deflection of the quartz photomask substrate 36 dueto its own weight, by controlling the pressure within the enclosedspace, which is measured by a pressure sensor 51. To this end, asuitable pressure control device is provided to control the pressurewithin the air-tight space such that the pressure in the air-tight spaceis lower than the atmospheric pressure by a suitable difference, so asto reduce the deflection of the substrate 36. The scan-exposing devices120, 130 eliminate a need of increasing the thickness of the quartzphotomask substrate 36 to reduce its amount of deflection, even wherethe substrate 36 has a large size (e.g., 60 inches), making it possibleto reduce the cost of the quartz photomask substrate 36. Further, thedevices 120, 130 simplify the manufacture of the photomask substrate,resulting in a further reduction in the cost of manufacture of thequartz photomask substrate.

As shown in FIGS. 23 and 24, the scan-exposing devices 120, 130 includea spot scan-exposing optical module 50 for implementing the spot scanexposure without using the quartz photomask substrate 36. The spotscan-exposing optical module 50 corresponds to the spot scan-exposingoptical system, and is interposed between the photomask substrate 36 andthe glass substrate 49, so that the glass substrate 49 is subjected tothe spot scan exposure to a ultraviolet radiation transmitted through anoptical fiber. The width of the spot scan exposure by the optical module50 can be adjusted as needed. Reference sign 46 in FIGS. 23 and 24denotes a pellicle provided to prevent adhesion of foreign matters tothe photomask substrate 36.

The yield ratio of the liquid crystal display can be improved by: firstimplementing the photomask scan exposure of the entire surface of theglass substrate 49 to the ultraviolet radiation by the photomaskscan-exposing means through the quartz photomask substrate 36, with thedensity of the ultraviolet radiation being lowered so as to remove onlya portion of the thickness of a photoresist 48; and then implementingthe spot scan exposure of the glass substrate 49 by the spotscan-exposing means using the spot scan-exposing optical module 50. Inthe photomask scan exposure to the reduced density of the ultravioletradiation, the required patterning resolution of the photoresist rangesfrom about 3 μm to about 10 μm. In the spot scan exposure, on the otherhand, the required photoresist patterning resolution is as low as about100 μm. To improve the yield ratio, therefore, the photomask scanexposure of the glass substrate 49 which requires the higher resolvingpower must be implemented before dust is deposited on the glasssubstrate 49.

The compensation for the deflection of the photomask substrate 36 due toits own weight must be dynamically effected to hold the flatness of thesubstrate 36 within about ±15 μm from the horizontal plane, by using alaser displacement meter or gage or a digital differential pressuregage. The accuracy of the compensation must be changed as needed,depending upon the depth of focus of a projection lens 47 and therequired resolving power. The red-laser displacement meters 44 shown inFIG. 23 or any other laser displacement meters may be used as the laserdisplacement meter.

In the third through sixth embodiments, the halftone exposure isfeedback-controlled according to a feedback control routine illustratedin the flow chart of FIG. 19. This feedback control routine is initiatedwith step S1 to apply a positive resist coating of 1.5-2.0 μm to theglass substrate 49. Step S1 is followed by step S2 to implement thehalftone exposure of the glass substrate 49. After the halftone-exposedportion of the positive resist coating is developed in step S3, thecontrol flow goes to step S4 to measure the actual thickness of thehalftone-exposed and developed portion of the positive resist coating.Step S4 is followed by step S7 to feedback-control the amount ofexposure of the positive resist coasting to the radiation, on the basisof the measured thickness of the halftone-exposed portion of thepositive resist coating, so that the measured thickness is held within apredetermined range between about 0.4 μm (4000 A) and about 0.6 μm (6000A). To this end, a suitable feedback control device is provided tofeedback-control the amount of exposure of the resist coasting to theradiation. During repeated implementation of steps S2, S3, S4 and S4,step S5 is implemented to determine whether the measured thickness fallswithin the predetermined range. If an affirmative decision is obtainedin step S5, the control flow goes to step S6 to perform a post-brakingoperation on the glass substrate 49. If the thickness measured apredetermined time after initiation of the feedback control in step S7considerably deviates from the lower or upper limit of the predeterminedrange, the positive resist coating is removed from the glass substrate49, and a positive resist coating is applied again to the glasssubstrate, and the halftone exposure must be effected again.

To assure a high degree of reproducibility of the halftone-exposedportion of the positive resist with high uniformity, it is desirable toinspect all of the workpieces of the glass substrate 49 in step S5. Thisinspection may be made by using film-thickness measuring means such as alaser thickness gage or a laser interferometer. In this specificexample, a white light interferometer 68 is used to accurately measure adifference between the actual values of the thicknesses of thenon-halftone-exposed portion and the halftone-exposed portion of thepositive resist coating. The principle of operation of the white lightinterferometer 68 is illustrated in FIG. 20. This white lightinterferometer 68 permits simultaneous measurement of the differencebetween the first and second thickness values of the above-indicated twopositive resist portions, and the second thickness value of thehalftone-exposed portion of the positive resist as measured from thesurface of the glass substrate 49 (from the resist-free area of thesubstrate). Accordingly, the required time for the measurement can bereduced.

The white light interferometer 68 shown in FIG. 20 is simple inoperation principle and construction, and has measuring accuracy ofabout 1 nm (10 A), and is available at a considerably low cost evenwhere the measuring system is arranged to measure a plurality of pointsat one time. Further, the required measuring time of the white lightinterferometer 68 is relatively short, it may be used as an in-lineinspection device. By feedback-controlling the condition of thephotomask scan exposure of the glass substrate 49 on the basis of anoutput of the white light interferometer 68, the halftone exposure canbe effected with a high degree of reproducibility, namely, without avariation in the thickness values of the positive resist pattern formedon the active matrix substrate.

While the scan-exposing devices 100 and 110 used in the third and fourthembodiments include the projection optical system 39 of multiple lenstype, the scan-exposing devices may use a mirror-reflection type opticalsystem.

The third through sixth embodiments using the scan-exposing devices 100,110, 120, 130 and the white light interferometer 68 to feedback-controlthe halftone exposure on the basis of the output of the white lightinterferometer 68 assure a high degree of reproducibility of thehalftone exposure, permitting a significant improvement of the yieldratio of the active matrix substrate. In these embodiments, the overallphotomask scan exposure of the active matrix substrate to the reduceddensity of radiation through the photomask substrate 36 is suitablycombined with the spot scan exposure of the active matrix substrate bythe spot scan-exposing means, to implement the halftone exposing stepwhich permits a considerable reduction in the variation of thecharacteristic of the thin-film transistor element, as compared with theconventional halftone exposing step. Thus, the present invention permitseconomical manufacture of an active matrix element with a high yieldratio, using an inexpensive photomask.

It is to be understood that the present invention may be embodied withvarious other changes, modifications and improvements, those skilled inthe art, without departing from the spirit and scope of the inventiondefined in the following claims:

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 9. (canceled)
 10. (canceled)
 11. (canceled) 12.(canceled)
 13. A scan-exposing device used in a process of manufacturinga liquid crystal display device including a pair of substrates at leastone of which is transparent, and a layer of a liquid crystal compositioninterposed between the pair of substrates, said scan-exposing devicebeing operable to scan-expose a photoresist applied to one of said pairof substrates, through a photomask having a desired light-shieldingpattern, said scan-exposing device comprising: a slide carrying said oneof the pair of substrates; photomask scan-exposing means forscan-exposing said photoresist while said photomask and said slide aremoved at a same speed in a same direction; and spot scan-exposing meansfor directly spot scan-exposing said photoresist without using saidphotomask, with a spot size ranging from about 0.1 mm to about 5 mm, andwherein said photomask scan-exposing means and said spot scan-exposingmeans are operable concurrently to expose said photoresist. 14.(canceled)
 15. A scan-exposing device according to claim 13, whereinsaid photomask scan-exposing means is operable to expose saidphotoresist through said photomask to a ultraviolet radiation whoseirradiation energy density is determined so as to remove only a portionof a thickness of said photoresist, and said spot scan-exposing meansincludes a spot scan-exposing optical system operable to expose thephotoresist to a spot light of a condensed ultraviolet radiation, andwherein said photomask scan-exposing means and said spot scan-exposingmeans are operable in one of two modes: consisting of: a mode in whichsaid spot scan-exposing means is operated after an operation of saidphotomask scan-exposing means; and a mode in which said spotscan-exposing means is operated to expose said photoresist in a directdirection while said photomask scan-exposing means is operated to exposesaid photoresist in said first direction, and said spot scan-exposingmeans is operated to expose said photoresist in a second directionperpendicular to said first direction after a photomask scan exposure ofsaid photoresist by said photomask scan-exposing means is completed overan entire surface areas of said photoresist.
 16. (canceled) 17.(canceled)